Featured Research

from universities, journals, and other organizations

Dopants dramatically alter electronic structure of superconductor

Date:

February 17, 2013

Source:

DOE/Brookhaven National Laboratory

Summary:

Doping dramatically alters the atomic-scale electronic structure of the parent of a high-temperature superconductor, with important consequences for the behavior of the current-carrying electrons, according to new research. The findings could potentially point to new ways to design superconductors with improved properties.

Share This

Scientists have found that the substitution of cobalt atoms into the crystal framework of an iron-based material—which is required to convert the material from a magnet into a superconductor—also introduces elongated impurity states at each cobalt atom (note the directional alignment of "twin" peaks around each cobalt atom in the electronic structure map). These elongated impurities then scatter electrons in an asymmetric way that explains many of the material's unusual properties, and could eventually lead to the design of new types of superconductors for practical applications in energy transmission and storage.

Over the last quarter century, scientists have discovered a handful of materials that can be converted from magnetic insulators or metals into "superconductors" able to carry electrical current with no energy loss -- an enormously promising idea for new types of zero-resistance electronics and energy-storage and transmission systems. At present, a key step to achieving superconductivity (in addition to keeping the materials very cold) is to substitute a different kind of atom into some positions of the "parent" material's crystal framework. Until now, scientists thought this process, called doping, simply added more electrons or other charge carriers, thereby rendering the electronic environment more conducive to the formation of electron pairs that could move with no energy loss if the material is held at a certain chilly temperature.

Related Articles

Now, new studies of an iron-based superconductor by an international team of scientists -- including physicists from the U.S. Department of Energy's Brookhaven National Laboratory and Cornell University -- suggest that the story is somewhat more complicated. Their research, published online in Nature Physics February 17, 2013, demonstrates that doping, in addition to adding electrons, dramatically alters the atomic-scale electronic structure of the parent material, with important consequences for the behavior of the current-carrying electrons.

"The key observation -- that dopant atoms introduce elongated impurity states which scatter electrons in the material in an asymmetric way -- helps explain most of the unusual properties," said J.C. Séamus Davis, the study's lead author, who directs the Center for Emergent Superconductivity at Brookhaven Lab and is also the J.G. White Distinguished Professor of Physical Sciences at Cornell University. "Our findings provide a new starting point for theorists trying to grapple with how these materials work, and could potentially point to new ways to design superconductors with improved properties," he said.

The researchers used a technique developed by Davis called spectroscopic imaging scanning tunneling microscopy to visualize the electronic properties around individual dopant atoms in the parent material, and to simultaneously monitor how electrons scatter around these dopants (in this case, cobalt).

Earlier studies had shown that certain electronic properties of the non-superconducting "parent" material had a strong directional dependence -- for example, electrons were able to move more easily in one direction through the crystal than in the perpendicular direction. However, in those studies, the signal of a strong directional dependence only appeared when the scientists put the dopants into the material, and got stronger the more dopants they added.

Before this, the assumption was that dopants simply added electrons, and that the material's properties -- including the emergence of superconductivity -- were due to some intrinsic characteristic (for example, the alternating alignments of electron spins on adjacent atoms) that resulted in a directional dependence.

"But the emergence of directional dependence of electronic properties as more dopants are added suggests that the strong directionality is a result of the dopants, not an intrinsic property of the material," Davis said. "We decided to test this idea by directly imaging what each dopant atom does to the nearby atomic-level electronic structure in these materials."

According to Davis, the current paper reports two very clear results:

At each cobalt dopant atom, there is an elongated impurity state -- a quantum mechanical state bound to the cobalt atom -- that aligns in a particular direction (the same for each cobalt atom) relative to the overall crystal.

These oblong, aligned impurity states scatter the current-carrying electrons away from the impurity state in an asymmetric way -- similar to the way ripples of water would propagate asymmetrically outward from an elongated stick thrown into a pond, rather than forming the circular pattern produced by a pebble.

"These direct observational findings explain most of the outstanding mysteries about how the electrical current moves through these materials -- for example, with greater ease perpendicular to the direction you would expect based solely on the characteristics of the parent material," Davis said. "The results show that the dopants actually do dramatic things to the electronic structure of the parent material."

"It's possible that what we've found could be similar to an effect dopants had on early semiconductors," Davis said. "Early versions of these materials, though useful, had nowhere near the performance as those developed after the 1970s, when scientists at Bell Labs figured out a way to move the dopant atoms far away from the electrons so they wouldn't mess up the electronic structure." That advance made possible all the microelectronics we now use every day, including cell phones, he said.

"If we find out the dopant atoms are doing something we don't want in the iron and even copper superconductors, maybe we can find a way to move them away from the active electrons to make more useful materials."

More From ScienceDaily

More Matter & Energy News

Featured Research

Mar. 31, 2015  Researchers have recorded the first direct observations of the micro-scale mechanisms behind the ability of skin to resist tearing. The results could be applied to the improvement of artificial skin, ... full story

Mar. 31, 2015  A year ago, researchers showed that their software endowed the walking robot Hector with a simple form of consciousness. Their new research goes one step further: they have now developed a software ... full story

Mar. 31, 2015  Landfills can make a profit from all their rotting waste and a new patent explains exactly how to make the most out of the stinky garbage sites. Decomposing trash produces methane, a landfill gas ... full story

Mar. 31, 2015  Scientists have achieved an unprecedented level of control over defects in liquid crystals that can be engineered for applications in liquid matter photonics. Sitting with a joystick in the comfort ... full story

Mar. 30, 2015  Neuroscientists are taking inspiration from natural motor control to design new prosthetic devices that can better replace limb function. Researchers have tested a range of brain-controlled devices ... full story

Mar. 30, 2015  Speaking in public is the top fear for many people. Now, researchers have developed an intelligent user interface for 'smart glasses' that gives real-time feedback to the speaker on volume modulation ... full story

Mar. 30, 2015  By studying the morphology and physiology of plants with tiny conical "hairs" or microfibers on the surface of their leaves, such as tomatoes, balsam pears and the flowers Berkheya purpea and Lychnis ... full story

Mar. 30, 2015  In the first study of its kind, scientists quantitatively show that electric vehicles will meet the daily travel needs of drivers longer than commonly assumed. They found that batteries that have ... full story

Mar. 30, 2015  One researcher has developed a clever solution to gather naturalistic driving data. For several years, she has been using a detailed driving simulator to study how participants respond to ... full story

Bionic Ants Could Be Tomorrow's Factory Workers

Reuters - Innovations Video Online (Mar. 30, 2015)  Industrious 3D printed bionic ants working together could toil in the factories of the future, says German technology company Festo. The robotic insects cooperate and coordinate their actions and movements to achieve a common aim. Amy Pollock reports.
Video provided by Reuters

Oct. 6, 2014  Using an ultrafast spectroscopy technique called time- and angle-resolved photoemission spectroscopy, researchers demonstrated a link between electron-boson coupling and high-temperature ... full story

Dec. 20, 2012  By doping a bismuth-based layered material with silver, Chinese scientists demonstrated that superconductivity is intrinsic to the new material rather than stemming from its ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.